1. Field of the Invention
The present invention relates to a melting furnace having preheating vessels for preheating raw materials, and more particularly to an electric are furnace which heats and melts preheated metal which has been charged into the electric furnace.
2. Description of the Related Arts
A melting furnace is ordinarily equipped with a tilting device to discharge melted materials and floating slag. Japanese Unexamined Patent Publication No. 4-309789 discloses a melting furnace having a tilting device. As shown in FIG. 6, the melting furnace has toothed gears 2 and driving gears 3. The toothed gears 2 are circumferentially placed on both sides of a melting furnace 1. The toothed gears are supported and engaged with driving gears 3. When a melt is discharged, the melting furnace is tilted by rotating the driving gears 3.
The melting furnace is provided with a furnace roof 4 and preheating towers 5a, 5b. The furnace roof 4 covers a material opening 1a which is arranged at the upper part of the melting furnace 1. The preheating towers are cylindrically shaped. The preheating towers 5a, 5b stand on the furnace roof 4. Exhaust gas from the melting furnace rises up through the furnace roof to the preheating towers. There a plurality of preheating chambers 6a, 6b appropriate in number to be placed upwardly from the bottom part of the preheating towers. At an upper part of the preheating chambers, there is provided a discharge opening 7 to discharge the exhaust gas, the discharge opening being connected to an exhaust duct.
Further, below each of the preheating chambers, there is a damper 8 which freely opens and closes for holding raw materials. At an upper-most part of the preheating chambers, there is provided a retaining chamber for retaining raw materials supplied appropriately therein from outside of the system.
In the case of a steel-making electric arc furnace using a formed electrode, it is necessary to decrease consumption of the electrode. Japanese Unexamined Utility Model Publication No. 6-2095 discloses a measure for decreasing the consumption of the electrode. As shown in FIG. 7, scrap storing sections 11 at two locations on a furnace roof are prepared and an upper electrode 12 is inserted between the two scrap storing sections. Above the scrap storing sections, there are exhaust gas ducts 13 and scrap transporters 14 respectively.
In this disclosure, arc generated from the upper electrode is surounded by scraps 15, and radiation heat transfer efficiency to the scraps is high. Therefore, the length of the upper electrode can be shortened. For this reason, the consumption of the electrode can be suppressed to be small.
The mentioned melting furnace having the preheating towers for preheating the raw materials can attain the improvement in melting efficiency but has a disadvantage.
As shown in FIG. 6, the melting furnace 11 includes a furnace roof 4 on a material feed opening 1a of the melting furnace 1 which is of a type of a hollow circular cylinder being horizontally laid. To make the melting furnace itself tilted smoothly at the time of the discharge of a melt, it is necessary to make the furnace roof circular arc-shaped. Thus, the preheating towers 5a, 5b placed standing on such high furnace roof occupies a highly tall level in space. Not only the structure of the preheating towers becomes highly tall but also a material trasporter transfering raw materials at such tall top of the preheating towers is required to be large-scaled and high-powered. Further, since a spacious gap between the melting furnace 1 and the furnace roof 4 is produced when the melt is discharged, gas containing dust or the like is scattered outside of the furnace and thus the work environment is worsened.
A portion, which is exposed within the melting furnace, of the electrode 10 inserted down to the melting furnace 1 from the top of the furnace roof 4 is longer in length than necessary. Therefore, the electrode 10 is exposed to a severely oxidized atmosphere and remarkably worn out due to oxidation.
The electric arc furnace of the Japanese Utility Model Publication No. 6-2095 is effective in suppressing the wear of the electrode, but has a problem here-below given.
In this electric arc furnace, there is no means for feeding supplied scraps into the electric arc furnace. The feeding of the scraps relies on natural drops of the scraps based on its dead weight. The operation has no problems so long as the scraps 16 are being smoothly fed from the two scrap storing sections into the electric arc furnace.
When, however, something wrong such as hanging within one of the scrap storing sections 11 happens, the feed of the scraps is one sided around the electrode 15. The melting of the scraps by the arc is thus non-uniform and the scraps are easily melted toward the electrode, which invites electrode damage.
Further, there is a difficulty in that the furnace roof 16 having the scrap storing section 11 has to be tilted integratedly together with the tilting of the electric arc furnace 17 when the melt is discharged. For this reason, the scrap storing sections 11 has to be emptied at the discharge of the melt. As the result of the emptying, it is impossible to preheat the scraps for the heat of the next melting.
In addition, due to lack of a combustion chamber, CO contained in exhast gas passing through the scrap storing section 11 fails to sufficiently be combusted into CO.sub.2, and thus, the exhaust gas is of a low temperature and harmful.